This application claims the priority of Swiss application 830/95-6 and PCT/CH96/00092, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a combustion grate as well as to a method for optimizing the operation of a combustion grate.
It is known that combustion chambers can be used preferably for burning various fuels, such as household waste, industrial waste, wood waste, solid, porous, and liquid fuels as well as fuels with high and low ignition performance. Such known combustion chambers are typically composed of a mechanical grate and by cooled or uncooled fireproof side walls.
Systems of this kind have the disadvantage that their operation are not optimal for all fuels, and therefore certain parts of such systems, especially parts of the grate, suffer from defects and short service lives.
Systems for cooling grate coatings are already known such as cooling the grate surface by using the combustion air flowing past in the air horns or forced cooling of the grate surface by the combustion air, which is forced through a chamber formed by the fire bar and a conducting panel, into the combustion chamber.
These known types of cooling systems depend upon the volume of combustion air, and the air outlets in the combustion chamber can be clogged by ashes, solid metals, or slag. As a result, the cooling of the respective surface is no longer ensured. This can lead to problems. At the same time, these types of cooling systems suffer from the disadvantage that the volume of combustion air has a function that is related primarily to the technology of the process and is not required to perform a cooling function. Changing the volume of combustion air as a function of the cooling effect is not always feasible. In this case also, the cooling effect of the grate surface is not ensured.
Water cooling for the grate surface is also known. The volume of water intended for cooling the grate surface keeps the grate surface at an approximately constant temperature, independently of the heating value of the fuel. Once again, this is disadvantageous when burning fuels with a low heating value because the combustion chamber loses heat. In this case, a higher cast-surface temperature would be advantageous for combustion.
DE-U-93 09 198 discloses a combustion grate in which a liquid or gaseous medium can be conducted through the fire bars to control their temperature. Depending on the requirement, the grate can either be cooled or heated. The grate in this case has the general form of a board, in other words a largely plane external surface. Within the grate, baffles can be provided to form a labyrinth for the temperature-controlling medium.
It has been found, however, that problems regarding the expansion of the tempering medium occur as a result of the very high temperature fluctuations that occur, especially when a large number of fire bars are to have their temperatures controlled at the same time.
An object of the present invention is to provide an improved combustion grate and method to remedy this disadvantage and to ensure reliable temperature control to optimize fuel combustion.
To this end, the combustion grate according to the present invention and the method for its optimum operation utilize whole or partial cooling by both gas and fluid via a regulating circuit.